More particularly, a first aspect of the present invention relates to a pump unit that includes a hydraulic pump, a pump case for accommodating the hydraulic pump and a center section connected to the pump case.
A hydraulic pump is used in various applications and in particular as the hydraulic pump adapted for operation in association with an actuator driven through the hydraulic effect. In this case, the hydraulic pump is connected to the actuator via a pair of hydraulic lines, and the output flow rate of hydraulic fluid discharged from the hydraulic pump is varied to cause the pressure difference between the pair of hydraulic lines, thereby driving the actuator. When the hydraulic pump is thus connected to the actuator via the pair of hydraulic lines so as to constitute a closed circuit, a charging mechanism is generally required to feed pressurized hydraulic fluid to the pair of hydraulic lines.
Specifically, the charging mechanism as required necessarily includes a charge line having a first end through which pressurized hydraulic fluid is fed into the pair of hydraulic lines, and a second end communicating with the pair of hydraulic lines, a checking valve for allowing the pressurized hydraulic fluid to flow from the charge line to the pair of hydraulic lines, while preventing the reverse flow.
For the hydraulic pump with the charging mechanism, it is desirable to reduce machining works for the reduction of the manufacturing cost, and/or improve an assembling efficiency in installing the check valve, or other works. However, there have not been made effective proposals in view of those points.
The first aspect of the present invention has been therefor conceived in consideration of the prior arts. It is an object of the first aspect of the present invention to provide a pump unit with the charging mechanism for feeding additional hydraulic fluid, which pump is used in association with the actuator driven through the hydraulic effect, and is capable of lowering the manufacturing cost and improving the assembling efficiency.
A second aspect of the present invention relates to a pump unit with first and second hydraulic pumps that is designed to be operated in association with an actuator driven through a hydraulic effect.
A hydraulic pump is used in various applications and in particular as the hydraulic pump adapted for operation in association with an actuator driven through the hydraulic effect. The description will hereinafter be made for the pump unit by taking for example the case where it includes the first and second hydraulic motors serving as the actuators that respectively drive the right and left drive wheels.
For example, U.S. Pat. No. 4,920,733 discloses a vehicle including first and second hydraulic pumps respectively connected via first and second hydraulic lines to the first and second hydraulic motors for driving the right and left drive wheels. In this vehicle, the first and second hydraulic motors respectively have outputs variable in response to the adjustment of the input/output flow rates of the first and second hydraulic pumps, thereby controlling the rotational speed and rotational direction of the right and left drive wheels.
The vehicle of the above arrangement has the first hydraulic pump and the second hydraulic pump separately arranged from one another, the former being operated in association with the first hydraulic motor, and the latter being operated in association with the second hydraulic motor. Such a separate arrangement of the hydraulic pumps involves a troublesome piping work between the first and second hydraulic pumps and the first and second hydraulic motors, a troublesome assembling work of the pump unit, and pose various other problems.
The second aspect of the present invention has been therefor conceived in consideration of the above prior art. It is an object of the second aspect of the present invention to provide a pump unit with the first and second hydraulic pumps that is capable of achieving the simplification of the piping work between the actuator and the hydraulic pumps, and the assembling work of the pump unit.
A third aspect of the present invention relates to a pump unit used for a vehicle with first and second hydraulic motors respectively connected to the right and left drive wheels, and includes first and second hydraulic pumps that are designed to be respectively operated in association with first and second hydraulic motors.
There are known arrangements of the above type described in, for example, U.S. Pat. No. 4,920,733. According to this US patent, a vehicle with first and second hydraulic motors respectively connected to the right and left drive wheels includes first and second hydraulic pumps respectively operable in association with the first and second hydraulic motors. In this vehicle, the first and second hydraulic motors respectively have outputs variable in response to the adjustment of the input/output flow rates of the first and second hydraulic pumps, thereby controlling the rotational speed and rotational direction of the right and left drive wheels.
The vehicle of the above arrangement has the first hydraulic pump and the second hydraulic pump which are separately arranged from one another, the former being operated in association with the first hydraulic motor, and the latter being operated in association with the second hydraulic motor. Such a separate arrangement of the hydraulic pumps poses various problems, such as troublesome mounting operation of the hydraulic pumps on the vehicle, and troublesome assembling operation.
The third aspect of the present invention has been therefor conceived in consideration of the above prior art. It is an object of the third aspect of the present invention to provide a pump unit used for the vehicle with the first and second hydraulic motors respectively connected to the right and left drive wheels, and including first and second axial piston pumps of a variable displacement type that is capable of having improved efficiencies in mounting the pump unit on the vehicle, and improved assembling efficiency.
A fourth aspect of the present invention relates to a pump unit with first and second hydraulic pumps that are respectively connected via first and second hydraulic lines to first and second actuators driven through a hydraulic effect.
A hydraulic pump is used in various applications and in particular as the hydraulic pump adapted for operation in association with an actuator driven through the hydraulic effect. The description will hereinafter be made for the pump unit by taking for example the case where it includes the first and second hydraulic motors serving as the actuators that respectively drive the right and left drive wheels.
For example, U.S. Pat. No. 4,920,733 discloses a vehicle including first and second hydraulic pumps respectively connected via first and second hydraulic lines to the first and second hydraulic motors for driving the right and left drive wheels. In this vehicle, the first and second hydraulic motors respectively have outputs variable in response to the adjustment of the input/output flow rates of the first and second hydraulic pumps, thereby controlling the rotational speed and rotational direction of the right and left drive wheels.
The vehicle disclosed in the above cited US patent has the first hydraulic pump and the second hydraulic pump separately arranged from one another, the former being operated in association with the first hydraulic motor, and the latter being operated in association with the second hydraulic motor. Such a separate arrangement of the hydraulic pumps invites a complicated structure of a feeding passage for feeding working hydraulic fluid from a reservoir tank to the first hydraulic line and the second hydraulic line, and poses various other problems.
The fourth aspect of the present invention has been therefor conceived in consideration of the above prior art. It is an object of the fourth aspect of the present invention to provide a pump unit with the first and second hydraulic pumps that are respectively connected via the first and second hydraulic lines to the first and second actuators driven through the hydraulic effect, and that is capable of achieving a simplified structure of the feeding passage for feeding working hydraulic fluid to the hydraulic lines extending between the actuators and the hydraulic pumps.
A fifth aspect of the present invention relates to a pump unit with first and second hydraulic pumps that are respectively connected via first and second hydraulic lines to first and second actuators driven through a hydraulic effect.
A hydraulic pump is used in various applications and in particular as the hydraulic pump adapted for operation in association with an actuator driven through the hydraulic effect. The description will hereinafter be made for the pump unit by taking for example the case where it includes the first and second hydraulic motors serving as the actuators that respectively drive the right and left drive wheels.
For example, U.S. Pat. No. 4,920,733 discloses a vehicle including first and second hydraulic pumps respectively connected via first and second hydraulic lines to the first and second hydraulic motors for driving the right and left drive wheels. In this vehicle, the first and second hydraulic motors respectively have outputs variable in response to the adjustment of the input/output flow rates of the first and second hydraulic pumps, thereby controlling the rotational speed and rotational direction of the right and left drive wheels.
The vehicle disclosed in the above cited US patent has the first hydraulic pump and the second hydraulic pump separately arranged from one another, the former being operated in association with the first hydraulic motor, and the latter being operated in association with the second hydraulic motor. Such a separate arrangement of the hydraulic pumps invites a complicated structure of a feeding passage for feeding working hydraulic fluid for an HST (hydrostatic transmission) from a hydraulic fluid tank to the first hydraulic line and the second hydraulic line, and poses various other problems.
As a further disadvantage, the working hydraulic fluid between the hydraulic pumps and the actuators may increase in temperature due to the load from the outside. Such an increase in temperature of the working hydraulic fluid may invite various problems such as lowering of the volumetric efficiency, or lowering of the axle revolution speed if the hydraulic motors are used as the actuators for driving the drive wheels of the vehicle, deteriorating of the durability. However, the above-cited US patent does not teach any solutions to limit the temperature of the working hydraulic fluid of the HST.
The fifth aspect of the present invention has been therefor conceived in consideration of the above prior art. It is an object of the fifth aspect of the present invention to provide a pump unit with the first and second hydraulic pumps that are respectively connected via the first and second hydraulic lines to the first and second actuators driven through the hydraulic effect, and that is capable of effectively limiting the increase in temperature of the working hydraulic fluid to be replenished to the hydraulic lines between the actuators and the hydraulic pumps.